Trans-activation of unspliced or partially spliced HIV RNAs by the REV regulatory protein is crucial for virus replication and is dependent on the sequence specific binding to a highly structured 244 nucleotide RRE RNA in the viral env gene. REV requires the presence of a nine nucleotide 5'- CACUAUGGG-3' RNA motif that must be presented as a stem-bulge-stem structure and must contain at least 2 Gs, one of which must be unpaired. But, RRE interaction is not an absolute requirement for REV function. REV will activate HIV mRNAs containing a heterologous MS2 phage operator sequence if directed to the operator via the RNA binding motif of the MS2 phage coat protein (MS-C) as a fusion protein. Mutation in the MS operator that abolished the coat protein binding in vitro rendered the mutant chimera non-responsive to the fusion protein in vivo. These studies imply that REV binding is the primary function of RRE, and cellular factors specifically reacting with RRE may not be necessary for REV function. While REV can be tethered to the viral RNAs by another protein, the structural integrity of REV was still required for optimal trans- activation. Two positive clones, RRBFI and RRBFII, which expressed major protein species of 43 and 45 kDal were obtained. These proteins were identical to the previously reported TAR binding protein(s), TRBP. We have extended our studies on the effect of HIV-1 NEF protein on cellular genes. HIV NEF protein decreases in the surface expression of CD4 receptor both in CD4+ T cells and non-lymphoid cells. The CD4 effect was due to accelerated recycling and degradation of the surface CD4. CD4 molecules which are retained in the ER and CD lacking the cytoplasmic domain are not regulated by NEF. Myristoylation of NEF was required for the effect on CD4. NEF effect on the CD4 in T cells may have profound effect(s) on T cell activation pathways. HIV-1 LTR linked NEF expression in transgenic mice was confined to skin and was associated with papillomatous skin lesions that varied in severity depending on the level of NEF expression.
